Donald Trump is not under investigation for firing FBI Director James Comey, the president's lawyer said, in seeming contradiction to a tweet the US leader had sent out earlier complaining of a "witch hunt" against him.

"Let me be clear here. The president is not and has not been under investigation for obstruction," lawyer Jay Sekulow from Trump's legal team told NBC's Meet The Press program.

The comment came after the president tweeted on Friday: "I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt."

Many took the message as a confirmation that Trump is under investigation, but Sekulow explained his client was talking about a different matter.

"The tweet from the president was in response to the five anonymous sources purportedly leaking info to the Washington Post," he said,referring to a recent story about special counsel Robert Mueller allegedly looking into whether Trump fired Comey last month in an attempt to obstruct an investigation into alleged Russian meddling in the US election.

"He (Trump) is not afraid of the investigation - there is no investigation," Sekulow said, stressing that "there is not an investigation of the president of the United States, period."

Sekulow made four TV appearances on Sunday to clarify the situation. In one, he told CBS's Face the Nation that "there has been no notification from the special counsel's office that the president is under investigation."

The US Justice Department has assigned Mueller to investigate the Russian meddling allegations.

The special counsel is looking for evidence to support claims that Trump's associates illegally colluded with Moscow during the president's victorious run for the White House last year.

The accusations have been repeatedly dismissed as groundless by both the Kremlin and the Trump team.